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FreeBSD-SA-14:20.rtsold                                     Security Advisory
                                                          The FreeBSD Project

Topic:          rtsold(8) remote buffer overflow vulnerability

Category:       core
Module:         rtsold
Announced:      2014-10-21
Credits:        Florian Obser, Hiroki Sato
Affects:        FreeBSD 9.1 and later.
Corrected:      2014-10-21 20:20:07 UTC (stable/10, 10.1-PRERELEASE)
                2014-10-21 20:20:36 UTC (releng/10.1, 10.1-RC2-p1)
                2014-10-21 20:20:36 UTC (releng/10.1, 10.1-RC1-p1)
                2014-10-21 20:20:36 UTC (releng/10.1, 10.1-BETA3-p1)
                2014-10-21 20:21:10 UTC (releng/10.0, 10.0-RELEASE-p10)
                2014-10-21 20:20:17 UTC (stable/9, 9.3-STABLE)
                2014-10-21 20:21:10 UTC (releng/9.3, 9.3-RELEASE-p3)
                2014-10-21 20:21:10 UTC (releng/9.2, 9.2-RELEASE-p13)
                2014-10-21 20:21:10 UTC (releng/9.1, 9.1-RELEASE-p20)
CVE Name:       CVE-2014-3954

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

As part of the stateless addess autoconfiguration (SLAAC) mechanism,
IPv6 routers periodically broadcast router advertisement messages on
attached networks to inform hosts of the correct network prefix,
router address and MTU, as well as additional network parameters such
as the DNS servers (RDNSS), DNS search list (DNSSL) and whether a
stateful configuration service is available.  Hosts that have recently
joined the network can broadcast a router solicitation message to
solicit an immediate advertisement instead of waiting for the next
periodic advertisement.

The router solicitation daemon, rtsold(8), broadcasts router
solicitation messages at startup or when the state of an interface
changes from passive to active.  Incoming router advertisement
messages are first processed by the kernel and then passed on to
rtsold(8), which handles the DNS and stateful configuration options.

II.  Problem Description

Due to a missing length check in the code that handles DNS parameters,
a malformed router advertisement message can result in a stack buffer
overflow in rtsold(8).

III. Impact

Receipt of a router advertisement message with a malformed DNSSL
option, for instance from a compromised host on the same network, can
cause rtsold(8) to crash.

While it is theoretically possible to inject code into rtsold(8)
through malformed router advertisement messages, it is normally
compiled with stack protection enabled, rendering such an attack
extremely difficult.

When rtsold(8) crashes, the existing DNS configuration will remain in
force, and the kernel will continue to receive and process periodic
router advertisements.

IV.  Workaround

No workaround is available, but systems that do not run rtsold(8) are
not affected.

As a general rule, SLAAC should not be used on networks where trusted
and untrusted hosts coexist in the same broadcast domain.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-14:20/rtsold.patch
# fetch http://security.FreeBSD.org/patches/SA-14:20/rtsold.patch.asc
# gpg --verify rtsold.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/rtsold.patch

c) Recompile rtsold.  Execute the following commands as root:

# cd /usr/src/usr.sbin/rtsold
# make && make install

4) Restart the affected service

To restart the affected service after updating the system, either
reboot the system or execute the following command as root:

# service rtsold restart

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r273412
releng/9.1/                                                       r273415
releng/9.2/                                                       r273415
releng/9.3/                                                       r273415
stable/10/                                                        r273411
releng/10.0/                                                      r273415
releng/10.1/                                                      r273414
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-3954>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:20.rtsold.asc>
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